Abstract
The use of approximate molecular orbital (MO) calculations [particularly complete neglect of differential overlap (CNDO)] as a tool in understanding chemical bonding in silicates is investigated. This requires first a detailed analysis of the parametrization employed by the CNDO theory when third row atoms are involved. The accuracy of the CNDO calculations is tested by calculations on the equilibrium bond lengths, orbital energies, and bond stretching force constants of simple third row molecules, for which we have experimental data and/or ab initio results. The effects of an optimization of the parameters in the theory on the calculated properties are then analyzed. The theory is subsequently applied to a sequence of silicate prototypes: silicic acid, H4SiO4, disiloxane, (SiH3) - O - (SiH3), and disilicic acid, (SiO3H3) - O - (SiO3H3). With proper tuning of the parameters, the CNDO method can be useful in further elucidating the details of the bonding in silicates.
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